i think we only want margo in pc requires

maint/ssg.pc.in

@@ -7,6 +7,6 @@ Name: ssg
 Description: Scalable Service Groups (SSG) interface for Mercury
 Version: 0.1
 URL: https://xgitlab.cels.anl.gov/sds/ssg
-Requires: mercury
+Requires: margo
 Libs: -L${libdir} -lssg
 Cflags: -I${includedir}